Step stool



FIG. 1 is a perspective view of a step stool showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a right-side elevational view thereof, with the left-side elevational view being a mirror image thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof. 

The ornamental design for a step stool, as shown and described. 